1. Field of the Invention
The present invention relates to apex seals for rotary piston engines, more particularly to an apex seal of ceramic material and an improved method for manufacturing the apex seal.
2. Description of the Prior Art
In the field of rotary piston engines, conventionally it has been known that a cast iron is chilled to form a hardened structure on the surface portion by applying an electronic beam as disclosed in U.S. Pat. No. 3,658,451. Such chilled cast iron has an excellent sliding property or wear resistance so that an apex seal of the chilled cast iron can match with trochoidal surface a rotor housing coated with Cr plating.
Recently, the rotary piston engine is required to produce a high power output causing an increase of heat load and temperature in the combustion chamber. Therefore it has been sought for the apex seal and trochoidal surface materials with a sufficient wear and heat resistance to threreby meet such high power output rotary piston engine.
Meanwhile, in the operation of the rotary piston engine, it takes a certain period until the apex seal wears to get to fit to the trochodal surface of the rotor housing. Therefore, in the initial stage of the operation of the rotary piston engine, there may occur an undesirable phenomenon, such as a reduction of compressed gas pressure in the combustion chamber resulting from poor fit property of the apex seal to the surface of the rotor housing. In order to improve the initial fit property between the sliding surface of the apex seal and the trochoidal surface of the rotor housing to thereby eliminate the above phenomenon, it has been proposed to apply a shot blasting treatment by carbon particles on the sliding surface of the apex seal so as to obtain a certain roughness in the sliding surface of the apex seal made of a hardened cast iron, so called chilled structure cast iron.